I think looking at smartphone owners as a whole to say look how many of them there are, is just as foolish as mis-managing and spending on their console games. Even if there was a billion Smartphone users around the world it would be hard to extrapolate from that how many are actually buying games. So far Square Enix and others have only done crummy ports of their games for those devices so the ROI was obviously fairly high, but what happens when they sink millions into development of a mobile game? And I don't even think that is their end goal in all of this, I think it is something far more sinister. I bet they feel that mobile users will lap up anything, especially with the name Square Enix on it, so they are most likely going to put the least amount effort possible into Mobile games and just assume people will buy them, and that's a terrible way to treat your brand.
One thing I have never understood is why won't Square Enix take a team and make a 2D Final Fantasy in the vein of FF6 and put that on XBLA, PSN, and even mobile devices, and heck PC? Talk about a ROI! These companies constantly complain about the rising costs of games, but they have no one to blame but themselves, because there are millions out there that would buy a sprite based game for $15-$20. Never understood this fascination that your game has to sell for $60 or it isn't worth it.